In our own U.S. Pat. No. 6,599,285, owned by the assignee of the present patent application, we disclosed a method for creating a computerized model which closely represents the surface of the cornea in three dimensions. A file representing sampled points in a corneal topography map of the surface of the cornea, for example the type produced by a corneal topography scanning machine, is read into a computer system running at a topological modeling computer program. The computer program then produces a surface model, which is displayed on the display of the computer system. Making use of the computer program, it is possible to simulate manipulations and operations upon the cornea. The model was used to simulate corneal ablation surgery on a patient's eye and to display the effect that the surgery would have on the eye. Using this approach, it was possible to demonstrate that a conventional intended operation would produce an irregular and undesirable surface. The model also made it possible to demonstrate that alternate approaches would have a better result. It was also possible to identify those patients that would not be good candidates for corneal ablation surgery. The same model was also used to determine the appropriate shape for a corrective contact lens with the pass-through surface that would conform closely to the surface of the cornea.
Making use of the computerized modeling techniques, we where able to demonstrate in our own U.S. Pat. Nos. 6,416,179 and 6,669,342 also owned by the assignee of the present patent application) that ablation surgery could be performed or corrective contact lenses could be shaped so as to respect the natural shape of the cornea, while still providing the necessary vision correction. This was accomplished by estimating the surface model with a plurality of best fit half-meridian characteristic arcs which originate from a central point on the corneal model and extend to its periphery, each arc being rotationally spaced from its neighbor. Minimal adjustments could then be made to the curvature of each arc to achieve a modified corneal shape (a modified model) required for vision correction. This permits ablation surgery with minimal material removal and the contact lens which fits extremely closely to the cornea.
Making use of surface modeling, we discovered that the points of focus of different areas of the typical cornea are so dispersed that the cornea exhibits a substantial amount of axial and radial focus scatter. In our published US Patent Application No. 2006/0189966, owned by the assignee of the present patent application, we disclosed a technique for manipulating the surface model so as to shift the points of focus of different areas towards a predefined axis, to produce a modified surface model. The surface of the cornea or contact lenses can then be the conformed to the modified surface model, substantially reducing focus scatter. This typically improves the quality of vision for corneal ablation patients and contact lens wearers. In this patent application, we also disclosed the concept of analyzing the cornea by plotting parameters at the different characteristic arcs, for example, a plot of the curvature of each of the arcs as a function of its angular displacement.
The disclosures of U.S. Pat. No. 6,599,285; U.S. Pat. No. 6,416,179; U.S. Pat. No. 6,669,342; and published US Patent Application No. 2006/0189966 are hereby incorporated by reference in their entireties.
Despite all of the benefits obtained from using surface modeling, we had still not realized its full potential as a diagnostic tool.
Keratoconus is a disorder of the eye in which the cornea develops a conical shape which becomes more pronounced as the condition progresses. Early detection of the disorder is desirable, not only to ensure treatment, but to avoid procedures, such as refractive surgery, which should not be undertaken for patients with this condition. For example, patients with keratoconus are prone to corneal ecstasia following LASIK surgery. Corneal ecstasia is a dangerous condition in which the cornea exhibits central bulging and structural failure. Accordingly, it would be desirable to be able to detect easily the earliest presence of keratoconus.